This paper presents a detailed statistical analysis comparing health-related quality of life (HRQL) between patients who underwent on-pump and off-pump coronary artery bypass graft (CABG) surgery. Using both the standardized SF-36 health survey and researcher-designed questions covering mental health, cognitive ability, social support, general health, and bodily pain, the study finds the two surgical groups are virtually indistinguishable across all measured dimensions. Multivariate data analysis is employed to identify and control for confounding demographic variables, including gender, education, ethnicity, age, and exercise habits. The findings support the null hypothesis that no clinically significant difference in HRQL exists between the two CABG procedures.
The paper demonstrates layered statistical triangulation: descriptive statistics are first presented for individual question categories, then cross-tabulated by demographic variables, and finally subjected to multivariate analysis. This progression ensures that apparent group differences are scrutinized from multiple analytical angles before conclusions are drawn. The explicit discussion of multivariate test statistics — Pillai's trace, Wilks' lambda, Hotelling's trace, and Roy's largest root — models transparency in quantitative reporting.
The paper opens by introducing the data analysis framework and instrumentation. It then proceeds section by section through the researcher-designed question categories (mental health, condition-specific, social support), followed by demographic profiling and multivariate validation. The SF-36 results, reliability coefficients, and component scores occupy the final analytical sections, with a closing synthesis linking all findings back to the central hypothesis.
SPSS was used to manage and calculate the researcher-designed data. Questions numbered 1–11 were administered as part of the SF-36 mental health inventory. As noted earlier, these questions provide a standard means of assessing clinical outcomes and mental health; however, they are insufficient on their own for assessing quality of life in patients undergoing on-pump and off-pump bypass surgery.
Questions 12–30 were research-developed and designed to provide a more accurate assessment of patient satisfaction with the two procedures. These questions were divided into categories representative of factors commonly associated with quality of life: Mental Health, Cognitive Ability, Social Support, General Health, and Bodily Pain. Demographic data is contained in questions 21–26 and will be used to identify confounding factors. For purposes of data analysis, the questions are analyzed by category and results compared for the two process controls (type of surgery) using descriptive analysis. Confounding factors are identified and reliability tests conducted using Cronbach's alpha reliability.
Mental health is perhaps the most defining concept of this study. As can be seen from the data presented in Table 2 and Figure 9, the mean for all three researcher-designed mental health questions was slightly higher in the off-pump patients than in the on-pump patients, but with a significance level set at α = 0.05 the two groups are virtually identical.
This statistical analysis holds true for individual question groups; however, these results must be compared across the sample population to determine whether they vary when demographic data is considered. For instance, women reported depression at more than four times the rate of men: 10.8% of men and 41.1% of women reported that, in the past year, they had "experienced four or more weeks during which they felt sad, blue or depressed, or when they lost all interest or pleasure in things that they enjoyed and cared about." Women who received on-pump CABG were slightly more depressed (5%) than women who received off-pump CABG. A previous study confirmed that women are more likely than men to experience postoperative depression after CABG surgery, attributable in part to poorer pre-operative health status (Ai, 1997). Several factors were not considered in this evaluation, and it is not known whether depression is a result of the type of CABG surgery or of other factors.
One subject of this study — reported to the researcher as deceased by the patient's daughter — was a man who committed suicide. He experienced first mild and then severe depression after undergoing on-pump CABG and was admitted to a psychiatric unit for treatment, where he spent two months. The day he was released, he died by self-inflicted injury. There had been no previous history of depression or any kind of mental illness. He had been a socially and physically active physician prior to his CABG surgery. This case is isolated, and it cannot be determined after the fact whether the suicide was a result of a decline in quality of life following CABG surgery or whether there may have been other unknown contributing factors.
Questions 13 and 14 refer to cognitive ability and memory. Questions 15 and 16 refer to bodily pain. Question 17 refers to health transition. The questions regarding surgical pain, current pain, and the frequency of arrhythmia are from the SF-36 portion of the survey. The tables and charts in this section pertain to five condition-specific questions: Cognitive Ability, Memory, Surgical Pain, Current Pain, and frequency of Arrhythmia. Scores range from worse to better for Cognitive Ability and Memory, from better to worse for the two Pain questions, and from very frequently to never for the Arrhythmia question.
As shown in Table 3, Figure 11, and Table 4, the off-pump patients fared slightly better in every category — except pain, which was evenly split as would be expected because the incisions are identical — but again, with a significance level set at α = 0.05 the two groups are virtually indistinguishable, and the differences noted are not clinically significant. The analysis of variance of condition-specific pain further supports this finding. There is no difference in the sternal incision between the on-pump and off-pump CABG procedures. The Cronbach's alpha reliability coefficients for the two researcher-developed pain questions are 0.987 and 0.937.
Questions 18, 19, and 20 addressed the level of social support patients received. The social support data showed that all respondents had either family members or pets living with them. Using Cronbach's alpha reliability, coefficients were calculated for the Mental Health Component Score and the family-pet support system; the reliability score was 0.977. One hundred percent of respondents had family members and/or pets living with them — not a single respondent lived alone. Since all respondents had a social support system in place, it is doubtful that lack of social support contributed to any depression found, but a multivariate analysis was conducted to confirm this. The social support data serves to rule out a confounding factor and demonstrates that social support was not a significant determinant of overall mental health in this patient population.
One patient wrote on her questionnaire that her family and friends would not let her get depressed, but she admitted having been depressed for a short period after surgery and noted that her sex life had been affected by the surgery. CABG surgery is particularly difficult for women when the saphenous vein is harvested rather than an artery. In addition to a scar down the middle of the chest, harvesting the vein requires an incision along the length of the leg, resulting in a scar approximately two feet long. This patient had been married only a couple of years when the surgery was performed. Depression in women may have more to do with self-image than with declining health, as existing studies suggest (Ai, 1997); however, this data was not a formal part of this study and would be of interest in further research.
The additional retrospective Likert-scale question — which asked, "The way I would have answered the questions in this survey before my heart operation would be" — was virtually split. The on-pump patients had a mean of 2.48 and the off-pump patients a mean of 2.53; once again slightly better but not clinically significant, with a Cronbach's alpha coefficient of 0.794 and significance set at α = 0.05.
Mental Health: On Question 12a, the mean for on-pump was 1.83 and for off-pump was 1.97. On Question 12b, the mean for on-pump was 1.80 and for off-pump was 1.86. On Question 12c, the mean for on-pump was 1.79 and for off-pump was 1.89. Because these three questions are dichotomous (yes = 1, no = 2), a higher mean indicates a stronger score.
Condition-Specific: For Question 13, the mean for on-pump was 2.83 and for off-pump was 3.06. For Question 14, the mean for on-pump was 2.74 and for off-pump was 2.97. For Question 17, the mean for on-pump was 4.23 and for off-pump was 4.33. These three questions used Likert scales moving from worse to better, so a higher mean indicates a stronger score. For Question 15, the mean for on-pump was 2.56 and for off-pump was 2.67. For Question 16, the mean for on-pump was 2.32 and for off-pump was 2.15. These two questions used Likert scales moving from better to worse, so a lower mean indicates a stronger score.
Social Support: For Question 18, the mean for on-pump was 2.20 and for off-pump was 1.97. For Question 19, the mean for on-pump was 1.84 and for off-pump was 2.02. These two Likert-scale questions moved from less to more, so a higher mean indicates a stronger score.
With a significance level set at α = 0.05, the two groups are virtually identical across all categories. Descriptive statistics on quality-of-life questions showed slight differences in some cases; however, none were clinically significant. Virtually no differences in quality of life were observed between the two surgical procedures.
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